@dexter If you `zfs set readonly=on mydataset` or likewise with `atime=off`, it doesn't change any of the child datasets. For example:
# zfs get atime rootvg/root
NAME PROPERTY VALUE SOURCE
rootvg/root atime on default
# zfs set atime=off rootvg
# zfs get atime rootvg/root
NAME PROPERTY VALUE SOURCE
rootvg/root atime on temporary

Pre-#OpenZFS on #FreeBSD the right thing happened and atime=off was inherited down the tree.